"These persons have been arrested for their Maoist links," Shivaji Bodakhe, joint commissioner of Pune police in western Maharashtra state, told AFP news agency, without giving further details.

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The government says Maoist rebels, who are active in several states, are India's biggest internal security threat.

The raids on Tuesday were in connection to an ongoing probe into the violence between lower caste Dalits and right-wing groups at Maharashtra's Bhima Koregaon village on December 31.

'Atmosphere of fear'

The crackdown was condemned by lawyers, academics, authors and rights watchdogs, with government critics accusing Prime Minister Narendra Modi's right-wing Bharatiya Janata Party (BJP) of attempting to silence its opponents.

"The nationwide crackdown on activists, advocates and human rights defenders is disturbing and threatens core human rights values," Amnesty International's Indian chapter and NGO Oxfam India said in a joint statement.

"The government should protect people's rights to freedom of expression, association, and peaceful assembly instead of creating an atmosphere of fear," said Amitabh Behar, CEO of Oxfam India.

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Booker-prize winning author Arundhati Roy, an outspoken critic of Modi, said the "perilous" arrests on "ludicrous charges" were an attempt to muzzle freedom ahead of next year's polls.

"The simultaneous state-wide arrests are a dangerous sign of a government that fears it is losing its mandate and is falling into panic," Roy told Press Trust of India news agency.

In July, media watchdog Reporters Without Borders warned of deteriorating press freedom in the world's largest democracy amid a sharp rise in online hate campaigns directed at critics of Modi's Hindu nationalist government.

The communist political movement in India started in the 1920s as an anti-colonial struggle when the country was still ruled by Britain, but the current phase of Maoist rebellion began in 2004.